Improve the forcing/promotion functions in `DepKindVTable` by Zalathar · Pull Request #153122 · rust-lang/rust

Zalathar · 2026-02-26T07:51:09Z

This is a bundle of changes to the two function pointers in DepKindVTable that are responsible for forcing dep nodes, or promoting disk-cached values from the previous session into memory.

The perf improvements to incr-unchanged and incr-patched are likely from skipping more of the “promotion” plumbing for queries that never cache to disk.

Zalathar · 2026-02-26T07:51:51Z

This is not fully-baked yet, but I want to run PR CI and perf to check for unanticipated problems.

@bors try @rust-timer queue

Improve the forcing/promotion functions in `DepKindVTable`

compiler/rustc_query_impl/src/dep_kind_vtables.rs

rust-bors · 2026-02-26T10:02:16Z

☀️ Try build successful (CI)
Build commit: dff6afa (dff6afa28aa02dfe76c0d36c5fc140333bf99233, parent: 1ed488274bec5bf5cfe6bf7a1cc089abcc4ebd68)

rust-timer · 2026-02-26T10:41:57Z

Finished benchmarking commit (dff6afa): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.8%	[-1.7%, -0.2%]	102
Improvements ✅ (secondary)	-1.2%	[-6.5%, -0.2%]	68
All ❌✅ (primary)	-0.8%	[-1.7%, -0.2%]	102

Max RSS (memory usage)

Results (primary -3.7%, secondary 4.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	8.2%	[8.1%, 8.2%]	2
Improvements ✅ (primary)	-3.7%	[-3.7%, -3.7%]	1
Improvements ✅ (secondary)	-3.4%	[-3.4%, -3.4%]	1
All ❌✅ (primary)	-3.7%	[-3.7%, -3.7%]	1

Cycles

Results (primary -3.1%, secondary -8.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.1%	[-3.2%, -3.1%]	2
Improvements ✅ (secondary)	-8.1%	[-18.7%, -2.7%]	7
All ❌✅ (primary)	-3.1%	[-3.2%, -3.1%]	2

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 492.161s -> 478.802s (-2.71%)
Artifact size: 395.78 MiB -> 397.55 MiB (0.45%)

Zalathar · 2026-02-27T01:17:23Z

r? nnethercote (or compiler)

nnethercote · 2026-02-27T01:57:27Z

Fantastic perf results!

I would like to eliminate GetQueryVTable if possible. I think it might be possible if each normal query's DepKindVTable had a pointer to its QueryVTable. But not in this PR.

@bors r+

rust-bors · 2026-02-27T01:57:30Z

📌 Commit 3b6451e has been approved by nnethercote

It is now in the queue for this repository.

Zalathar · 2026-02-27T02:47:06Z

I would like to eliminate GetQueryVTable if possible. I think it might be possible if each normal query's DepKindVTable had a pointer to its QueryVTable. But not in this PR.

Right now, GetQueryVTable is what allows DepKindVTable to not know about query key/value/cache types at all, because that knowledge is baked into the different generic instantiations of its function pointers instead.

So I currently don't see a way to usefully put a query-vtable pointer into DepKindVTable.

Zoxc · 2026-02-27T21:16:35Z

compiler/rustc_middle/src/dep_graph/mod.rs

+    /// True if a key can _potentially_ be recovered from a key fingerprint
+    /// with this style.
+    ///
+    /// For some key types, recovery is possible but not guaranteed.


This seems a bit misleading. Do we have any types where recovery will fail?

Yes, it's possible for DefId to fail recovery, for example.

I verified this by adding a panic to the failure path of one of the try_recover_key calls, and then running x test incremental.

- `force_from_dep_node` → `force_from_dep_node_fn` - `try_load_from_disk_cache` → `promote_from_disk_fn` This commit also inlines the wrapper function around `promote_from_disk_fn`.

rustbot · 2026-03-01T08:42:33Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

Zalathar · 2026-03-01T08:43:12Z

Rebased to fix trivial conflict.

@bors r=nnethercote

rust-bors · 2026-03-01T08:43:15Z

📌 Commit 08df254 has been approved by nnethercote

It is now in the queue for this repository.

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rust-bors bot pushed a commit that referenced this pull request Feb 26, 2026

Auto merge of #153122 - Zalathar:dep-kind-vtable, r=<try>

dff6afa

Improve the forcing/promotion functions in `DepKindVTable`

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 26, 2026

Zalathar commented Feb 26, 2026

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compiler/rustc_query_impl/src/dep_kind_vtables.rs Outdated Show resolved Hide resolved

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 26, 2026

Zalathar force-pushed the dep-kind-vtable branch 3 times, most recently from 2aba5f0 to 3b6451e Compare February 26, 2026 22:56

rustbot assigned nnethercote Feb 27, 2026

Zalathar marked this pull request as ready for review February 27, 2026 01:17

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 27, 2026

nnethercote approved these changes Feb 27, 2026

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rust-bors bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 27, 2026

Zoxc reviewed Feb 27, 2026

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rust-bors bot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Mar 1, 2026

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rust-bors bot removed the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Mar 1, 2026

Zalathar added 4 commits March 1, 2026 19:41

Rename the function pointers in DepKindVTable

c0e7a43

- `force_from_dep_node` → `force_from_dep_node_fn` - `try_load_from_disk_cache` → `promote_from_disk_fn` This commit also inlines the wrapper function around `promote_from_disk_fn`.

Avoid some trivial wrapper closures in DepKindVTable

4284edc

Explain why some queries don't support forcing/promotion

f7ac426

Don't try to promote queries that never cache to disk

08df254

Zalathar force-pushed the dep-kind-vtable branch from 3b6451e to 08df254 Compare March 1, 2026 08:42

rust-bors bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 1, 2026

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rust-timer commented Feb 26, 2026

Overall result: ✅ improvements - no action needed

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Zalathar commented Feb 26, 2026 •

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